According to the API Spec 5CT standard, K55 is a Group 1 general-purpose carbon steel grade with a specified yield strength ranging from 55,000 to 80,000 psi and a minimum tensile strength of 95,000 psi, which is higher than that of the J55 grade.
It is primarily utilized for casing and tubing in shallow to medium-depth oil and gas wells, where its main function is to serve as a reliable structural barrier to prevent wellbore collapse and as a production conduit in non-corrosive (sweet service) environments, providing a cost-effective solution for maintaining well integrity and isolating formation pressures.
API 5CT K55 Casing and tubing Chemical Composition
| C | Mn | Mo | Cr | Ni | Cu | Ti | P | S | Si | V | Al | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Min | - | - | - | - | - | - | - | - | - | - | - | - |
| Max | - | - | - | - | - | - | - | 0.030 | 0.030 | - | - | - |
API 5CT K55 OCTG Pipe Mechanical Properties
| Tensile Strength | 655 MPa min | 95,000 psi min |
| Yield Strength | 379 MPa min | 552 MPa max |
| 55,000 psi min | 80,000 psi max | |
| Total Elongation Under Load | 0.500 % | - |
| Hardness | - | - |
API 5CT K55 Casing vs. Tubing
| Feature | API 5CT K55 Casing | API 5CT K55 Tubing |
| Primary Function | Lines the wellbore to provide structural support, prevent collapse, and isolate geological formations. | Placed inside the casing to serve as the main conduit for transporting oil and gas to the surface. |
| Installation | Installed against the wellbore wall; usually permanently fixed with cement. | Suspended within the casing; generally not cemented and can be retrieved or replaced. |
| Outside Diameter (OD) | 4-1/2" - 20" (114.3mm - 508.0mm) | 1.050" - 4-1/2" (26.7mm - 114.3mm) |
| Common Connections | BTC (Buttress), LTC (Long Round), STC (Short Round). | EUE (External Upset), NUE (Non-Upset), IJ (Integral Joint). |
| Wall Thickness | Typically thicker to withstand external formation and collapse pressures. | Relatively thinner, designed primarily to handle internal flow and pressure. |
| Length Range | Commonly Range 2 (25–34 ft) and Range 3. | Commonly Range 2 (28–32 ft). |
| Service Environment | Non-corrosive (Sweet Service) in shallow to medium-depth wells. | Non-corrosive (Sweet Service) production operations. |
API 5CT K55 Oilfield Casing Pipes Dimensions And Weight
| Size | Weight | Outside Diameter | Wall Thickness | End Finish | ||||||
| Grade | ||||||||||
| in | mm | in | mm | J55K55 | L80 | N80 | C90T95 | P110 | ||
| 4 1/2 | 9.50 | 4.500 | 114.3 | 0.205 | 5.21 | PS | – | – | – | – |
| 10.50 | 0.224 | 5.69 | PSB | – | – | – | – | |||
| 11.60 | 0.250 | 6.35 | PSLB | PLB | PLB | PLB | PLB | |||
| 13.50 | 0.290 | 7.37 | – | PLB | PLB | PLB | PLB | |||
| 15.10 | 0.337 | 9.56 | – | – | – | – | PLB | |||
| 5 | 11.50 | 5.00 | 127.00 | 0.220 | 5.59 | PS | – | – | – | – |
| 13.00 | 0.253 | 6.43 | PSLB | – | – | – | – | |||
| 15.00 | 0.296 | 7.52 | PSLB | PLB | PLB | PLBE | PLB | |||
| 18.00 | 0.362 | 9.19 | – | PLB | PLB | PLBE | PLB | |||
| 21.40 | 0.437 | 11.10 | – | PLB | PLB | PLB | PLB | |||
| 23.20 | 0.478 | 12.14 | – | PLB | ||||||
| 24.10 | 0.500 | 12.70 | – | PLB | ||||||
| 5 1/2 | 14.00 | 5.500 | 139.7 | 0.244 | 6.20 | PS | – | – | – | – |
| 15.50 | 0.275 | 6.98 | PSLB | – | – | – | – | |||
| 17.00 | 0.304 | 7.72 | PSLB | PLB | PLB | PLBE | PLB | |||
| 20.00 | 0.361 | 9.17 | – | PLB | PLB | PLBE | PLB | |||
| 23.00 | 0.415 | 10.54 | – | PLB | PLB | PLBE | PLB | |||
| 6 5/8 | 20.00 | 6.625 | 168.28 | 0.288 | 7.32 | PSLB | – | – | – | – |
| 24.00 | 0.352 | 8.94 | PSLB | PLB | PLB | PLBE | PLB | |||
| 28.00 | 0.417 | 10.59 | – | PLB | PLB | PLBE | PLB | |||
| 32.00 | 0.475 | 12.06 | – | PLB | PLB | PLBE | PLB | |||
| 7 | 17.00 | 7.00 | 177.80 | 0.231 | 5.87 | – | – | – | – | – |
| 20.00 | 0.272 | 6.91 | PS | – | – | – | – | |||
| 23.00 | 0.317 | 8.05 | PSLB | PLB | PLB | PLBE | – | |||
| 26.00 | 0.362 | 9.19 | PSLB | PLB | PLB | PLBE | PLB | |||
| 29.00 | 0.408 | 10.36 | – | PLB | PLB | PLBE | PLB | |||
| 32.00 | 0.453 | 11.51 | – | PLB | PLB | PLBE | PLB | |||
| 35.00 | 0.498 | 12.65 | – | PLB | PLB | PLBE | PLB | |||
| 38.00 | 0.540 | 13.72 | – | PLB | PLB | PLBE | PLB | |||
| 7 5/8 | 24.00 | 7.625 | 193.68 | 0.300 | 7.62 | – | – | – | – | – |
| 26.40 | 0.328 | 8.33 | PSLB | PLB | PLB | PLBE | PLB | |||
| 29.70 | 0.375 | 9.52 | – | PLB | PLB | PLBE | PLB | |||
| 33.70 | 0.430 | 10.92 | – | PLB | PLB | PLBE | PLB | |||
| 39.00 | 0.500 | 12.70 | – | PLB | PLB | PLBE | PLB | |||
| 42.80 | 0.562 | 14.27 | – | PLB | PLB | PLB | PLB | |||
| 45.30 | 0.595 | 15.11 | – | PLB | PLB | PLB | PLB | |||
| 47.10 | 0.625 | 15.88 | – | PLB | PLB | PLB | PLB | |||
| 8 5/8 | 24.00 | 8.625 | 219.08 | 0.264 | 6.71 | PS | – | – | – | – |
| 28.00 | 0.304 | 7.72 | – | – | – | – | – | |||
| 32.00 | 0.352 | 8.94 | PSLB | – | – | – | – | |||
| 36.00 | 0.400 | 10.16 | PSLB | PLB | PLB | PLBE | PLB | |||
| 40.00 | 0.450 | 11.43 | – | PLB | PLB | PLBE | PLB | |||
| 44.00 | 0.500 | 12.70 | – | PLB | PLB | PLBE | PLB | |||
| 49.00 | 0.557 | 14.15 | – | PLB | PLB | PLBE | PLB | |||
| 9 5/8 | 32.30 | 9.625 | 244.48 | 0.312 | 7.92 | – | – | – | – | – |
| 36.00 | 0.352 | 8.94 | PSLB | – | – | – | – | |||
| 40.00 | 0.395 | 10.03 | PSLB | PLB | PLB | PLBE | – | |||
| 43.50 | 0.435 | 11.05 | – | PLB | PLB | PLBE | PLB | |||
| 47.00 | 0.472 | 11.99 | – | PLB | PLB | PLBE | PLB | |||
| 53.50 | 0.545 | 13.84 | – | PLB | PLB | PLBE | PLB | |||
| 58.40 | 0.595 | 15.11 | – | PLB | PLB | PLB | PLB | |||
| 10 3/4 | 32.75 | 10.75 | 273.05 | 0.279 | 7.09 | – | – | – | – | – |
| 40.50 | 0.350 | 8.89 | PSB | – | – | – | – | |||
| 15.50 | 0.400 | 10.16 | PSB | – | – | – | – | |||
| 51.00 | 0.450 | 11.43 | PSB | PSB | PSB | PSBE | PSB | |||
| 55.50 | 0.495 | 12.57 | – | PSB | PSB | PSBE | PSB | |||
| 60.70 | 0.545 | 13.84 | – | – | – | PSBE | PSB | |||
| 65.70 | 0.595 | 15.11 | – | – | – | PSB | PSB | |||
| 13 3/8 | 48.00 | 13.375 | 339.73 | 0.330 | 8.38 | – | – | – | – | – |
| 54.50 | 0.380 | 9.65 | PSB | – | – | – | – | |||
| 61.00 | 0.430 | 10.92 | PSB | – | – | – | – | |||
| 68.00 | 0.480 | 12.19 | PSB | PSB | PSB | PSB | PSB | |||
| 72.00 | 0.514 | 13.06 | – | PSB | PSB | PSB | PSB | |||
| 16 | 65.00 | 16 | 406.40 | 0.375 | 9.53 | – | – | – | – | – |
| 75.00 | 0.438 | 11.13 | PSB | – | – | – | – | |||
| 84.00 | 0.495 | 12.57 | PSB | – | – | – | – | |||
| 109.00 | 0.656 | 16.66 | P | P | P | – | P | |||
| 18 5/8 | 87.50 | 18.625 | 473.08 | 0.435 | 11.05 | PSB | – | – | – | – |
| 20 | 94.00 | 20 | 508.00 | 0.438 | 11.13 | PSLB | – | – | – | – |
| 106.50 | 0.500 | 12.70 | PSLB | – | – | – | – | |||
| 133.00 | 0.635 | 16.13 | PSLB | – | – | – | – | |||
Connection & Thread Types for API 5CT K55
K55 belongs to API Group 1 and is commonly used in shallow to medium-depth wells. Its connections cover standard forms for both Casing and Tubing.
Casing Connections
BTC (Buttress Thread Connection):
Features: The thread cross-section is trapezoidal. It offers high tensile strength and load-bearing capacity. It is currently the most mainstream connection for K55 casing.
LTC (Long Round Thread Connection):
Features: 8 threads per inch with a longer thread length. Its sealing performance and tensile strength are superior to STC, making it suitable for medium depths.
STC (Short Round Thread Connection):
Features: Shorter thread length with relatively lower strength. It is typically used for shallow or non-critical well sections in low grades like K55.
Tubing Connections
EUE (External Upset End):
Features: The pipe ends are forged (upset) to increase thickness, making the joint strength higher than the pipe body. This is the most common connection for K55 tubing.
NUE (Non-Upset End):
Features: The pipe ends are not thickened, and threads (usually 10 round threads) are machined directly onto the pipe. It is rarely used today due to its lower joint strength.
Premium Connections
While API standard threads are most common for K55, Premium Connections (proprietary gas-tight threads) can be machined onto K55 pipe bodies for applications requiring high gas-tight integrity.
Quality Inspection for API 5CT K55
Chemical Analysis: Strict Phosphorus (P) and Sulfur (S) limits to ensure material toughness and weldability.
Mechanical Testing: Verifying Yield Strength (55k-80k psi), Tensile Strength (min 95k psi), and elongation.
Dimensional & Drift: Precise OD/Wall tolerance check and Drift Mandrel test to ensure internal clearance for tools.
Hydrostatic Test (Mandatory): 100% joint-by-joint pressure test (min 5 seconds) to verify seal and burst integrity.
NDT & Gauging: Ultrasonic (UT) or Magnetic Particle (MPI) testing for cracks, combined with professional thread gauging.
Visual Inspection: Comprehensive surface screening for defects like laps, scabs, or mechanical damage.
API 5CT K55 Casing and Tubing factory
API 5CT K55 oil country tubular goods Test equipments
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GNEE API 5CT K55 Casing and tubing suppliy range
• Standards: API SPEC 5CT
• Grades: K55
• PSL level: PSL1, PSL2, PSL3
• Stock Available: Yes
• Manufacturing process: Seamless, ERW
• P110 Casing and Tubing Outer Diameter: 2-3/8", 2-7/8", 3-1/2", 4-1/2", 5-1/2", 6-5/8", 7", 7-5/8", 7-3/4", 8-5/8", 9-5/8", 10-3/4", 11-3/4", 13-3/8", 16", 18-5/8", 20"
• Thickness: 4 LB/FT to 106.59 LB/FT, 0.244" to 0.875"
• Coupling thread: BTC, Buttress (Regular, Special bevel or special clearance), LTC, STC, premium connections threads.
• Length: R1, R2, R3, customized
FAQ
What is K55 material grade?
K55 is an API 5CT general-purpose carbon steel grade used for casing and tubing in oil and gas wells.
What is the difference between J55 and K55 casing?
| Item | J55 | K55 |
|---|---|---|
| Chemical Composition | Both P and S ≤0.030%, same requirement | Both P and S ≤0.030%, same requirement |
| Yield Strength | 379-552 MPa (same range for both) | 379-552 MPa (same range for both) |
| Tensile Strength | ≥552 MPa | ≥655 MPa (significantly higher) |
| Minimum Elongation | Slightly higher than K55 | Slightly lower than J55 |
| Impact Property | Same requirement for the same size | Same requirement for the same size |
| Heat Treatment Delivery Status | Usually delivered in normalized or quenched and tempered condition | Can be delivered in as-rolled condition |
| Interchangeability | Cannot be used as a substitute for K55 | Can be used as a substitute for J55 |
What is the meaning of K55?
In the API 5CT standard, the name K55 identifies the mechanical strength of the steel:
K: The letter designated by API to identify this specific Group 1 steel grade. While it shares the same yield strength as J55, K has a higher minimum tensile strength.
55: Represents the Minimum Yield Strength of 55,000 psi (55 ksi).